Multilayer golf ball and composition

ABSTRACT

The present invention is directed towards a multi-layer golf ball which comprises a core, a cover layer and at least one intermediate layers disposed between the core and cover, wherein the intermediate layer comprises an ethylene methacrylic/acrylic acid copolymer and optionally, a second thermoplastic component such as polyetherester block copolymer, polyesterester block copolymer, polyetheramide block copolymer, dynamically vulcanized thermoplastic elastomer, functionalized styrene-butadiene elastomer, thermoplastic polyurethane, thermoplastic polyesters, metallocene polymer or blends thereof and a filler such as zinc oxide, titanium dioxide or blends thereof. Further, in a preferred embodiment, the core has a compression less than 60, the finished ball has a COR (@ 125 ft/sec) of about 0.795 to about 0.815, the intermediate layer has a specific gravity of greater than about 1.2 and the cover has a Shore D hardness of about 60 to about 72.

This application is continuation-in-part of U.S. patent application Ser. Nos. 08/603,057, 08/606,373, 08/706,008 and 08/746,362 filed Feb. 16, 1996, Feb. 23, 1996, Aug. 30, 1996 and Nov. 8, 1996, respectively, which have issued as U.S. Pat. Nos. 5,759,676, 5,721,304, 5,813,923 and 5,810,678, respectively, the disclosures of which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates generally to golf balls, and more specifically, to a multilayer golf ball. In particular, this invention relates to a golf ball having a core, a cover and at least one intermediate layer disposed between the core and cover, wherein the intermediate layer is formed from a blend comprising an ethylene methacrylic/acrylic acid copolymer. The multilayer golf balls of the present invention have been found to provide the distance and durability characteristics approaching that of a conventional two piece ball while also providing the feel and "click" similar to that of a conventional wound golf ball.

BACKGROUND OF THE INVENTION

Conventional golf balls can be divided into two general types or groups: two piece balls or three piece balls, the latter including wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.

Balls having a two piece construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Two piece balls are made with a single solid core, usually formed of a crosslinked rubber, which is encased by a cover material. Typically the solid core is formed of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents and is covered by a tough, cut-proof blended cover. The cover is generally formed of a material such as SURLYN®, which is a trademark for an ionomer resin produced by DuPont. The combination of the core and cover materials provide a "hard" ball that is virtually indestructible by golfers. Further, such a combination imparts a high initial velocity to the ball which results in improved distance. Because the materials of which the ball is formed are very rigid, two piece balls have a hard "feel" when struck with a club. Likewise, due to their hardness, these balls have a relatively low spin rate which provides greater distance.

At the present time, the wound ball remains the preferred ball of the more advanced players due to its spin and feel characteristics. Wound balls typically have either a solid rubber or liquid center core around which many yards of a stretched elastic thread or yarn are wound. The wound core is then covered with a durable cover material such as a SURLYN® or similar material or a softer cover such as Balata or polyurethane. Wound balls are generally softer and provide more spin than non-would balls, which enables a skilled golfer to have more control over the ball's flight and final position. Particularly, with approach shots into the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.

Manufacturers place a great deal of emphasis on producing golf balls that consistently achieve the highest possible initial velocity without exceeding the United States Golf Association's (USGA) limit of 77.7 m/s (255 ft/s) when struck with a driver with a clubhead speed of 39.6 m/s (130 ft/s). In an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls having initial velocities as close as possible to the USGA initial velocity maximum, and yet maintain an acceptable feel and compression.

A number of patents have been issued which are directed towards modifying the properties of a conventional two piece ball by altering the typical single layer core and single cover layer construction to provide a multi-layer ball having such as a dual cover layer, dual core layer and/or a ball having a mantle layer disposed between the cover and the core. The inventions disclosed in the prior art patents are directed towards improving a variety such golf balls' physical properties and "in-play" characteristics.

Several patents are directed towards improving the carry distance of such balls. For example, U.S. Pat. No. 4,863,167 relates to a three piece solid golf ball having increased flight distance, wherein the ball has a center portion and an outer layer formed from a rubber composition, wherein the outer layer is harder than the center portion and further contains a gravity filler so as to impart a higher specific gravity to the outer layer than that of the center portion. U.S. Pat. No. 5,184,828 relates to a solid three-piece golf ball having improved rebound characteristics and carry distance while maintaining an adequate spin rate, wherein these characteristics are obtained by controlling the size of the polybutadiene inner core and outer layer as well as their specific gravity and hardness. According to the '828 patent, the key to obtaining the desired rebound characteristics is that the maximum hardness (42-62 Shore D) must be located at the interface between the core and the mantle and the hardness must then decrease both inwardly and outwardly. U.S. Pat. No. 4,714,253 is also directed towards a three-piece golf ball having an excellent rebound coefficient. This golf ball has a core with a Shore C hardness of 57-80 in its center, but not more than 83 at a distance between 5-10 mm from its center and an outer layer with a Shore C hardness of 70-83.

Additionally, there are a number of patents directed towards improving the spin, click and feel of solid balls while maintaining the distance provided by the solid construction. For example, U.S. Pat. No. 5,072,944 discloses a three-piece solid golf ball having a center layer and an outer layer which are prepared from a rubber composition, wherein it is desirable that the center core layer is softer than the outer layer, the layers having a hardness (Shore C) of 25-50 and 70-90, respectively.

U.S. Pat. No. 4,625,964 relates to a solid golf ball having a polybutadiene rubber core of a diameter not more than 32 mm, a polybutadiene rubber intermediate layer having a specific gravity of lower than that of the core material, and a cover. U.S. Pat. No. 4,650,193 is directed towards a solid golf ball having a core comprising a central portion and an integral outer layer, wherein the core is a curable elastomer such as polybutadiene which is treated with a cure altering agent to soften an outer layer of the core, to produce a central layer with a hardness (Shore C) of greater than 75 and an outer layer with a hardness (Shore A) of less than 80.

U.S. Pat. No. 4,848,770 discloses a non-wound three-piece golf ball which includes a core of a highly filled synthetic rubber or polymeric material, an intermediate mantle of an unfilled synthetic rubber and a cover. The core and intermediate mantle have a hardness of between 50-95 Shore D. U.S. Pat. No. 5,002,281 is directed towards a three-piece solid golf ball which has an inner core having a hardness of 25-70 (Shore C), an outer shell having a hardness of 80-95 (Shore C) and a cover. Further, the specific gravity of the inner core must be greater than 1.0, but less than or equal to that of the outer shell, which must be less than 1.3.

The prior art discloses a variety of materials other than polybutadiene for use as intermediate layers. For example, U.S. Pat. No. 5,253,871 concerns a golf ball having a three piece structure comprising an elastomer core, an intermediate layer of a thermoplastic material containing at least 10% of ether block copolymer, preferably blended with an ionomer, and a thermoplastic cover. U.S. Pat. No. 5,681,898 is directed to a multilayer golf ball having a conventional polybutadiene core, an ionomer cover and an intermediate layer formed from a blend of an ethylene methacrylic acid copolymer and a vulcanizate formed from polybutadiene and a peroxide curing agent. U.S. Pat. Nos. 5,439,227 and 5,556,098 both disclose multilayer golf balls which have a conventional polybutadiene core, conventional covers and an intermediate layer formed from a polyetherester block copolymer filled with zinc oxide and optionally blended with an ionomer.

Further, there are also several patents which are directed to golf balls having multiple cover layers. For example U.S. Pat. No. 4,431,193 relates to a golf ball having a multilayer cover wherein the inner layer is a hard, high flexural modulus ionomer resin and the outer layer is a soft, low flexural modulus ionomer resin, and wherein either or both layers may comprise a foamed ionomer resin. U.S. Pat. No. 5,314,187 also relates to golf balls having a multiple layer cover, wherein the outer layer is molded over the inner layer and comprises a blend of balata and an elastomer and the inner layer is an ionomer resin. U.S. Pat. No. 4,919,434 is directed towards a golf ball having a cover which comprises an inner layer and an outer layer each of which comprise a thermoplastic resin, preferably the layers comprise of materials that are capable of fusion bonding with each other.

However, none of the patents discussed above disclose a multilayer ball which employs the materials and has the improved physical properties as disclosed herein.

SUMMARY OF THE INVENTION

The present invention is directed towards an improved multilayer golf ball which comprises a core, a cover layer and at least one intermediate layer disposed between the core and cover layer, wherein the intermediate layer is formed from a blend comprising an ethylene methacrylic or acrylic acid copolymer, and wherein such golf balls provide a soft feel similar to a conventional wound ball, while also providing the distance, durability, spin rates and relative ease of manufacturing of a conventional two piece ball.

The present invention is further directed to a multilayer golf ball which comprises a core, at least one cover layer and at least one intermediate layer disposed between the core and cover layer wherein: the core is formed from a blend comprising polybutadiene and has a COR of about 0.795 to about 0.815 measured at 125 ft./sec and a compression of no greater than about 60; at least one cover layer has a Shore D hardness of about 60 to about 68; and at least one intermediate layer is formed from a blend comprising an ethylene methacrylic or acrylic acid copolymer. optionally, the intermediate layer blend further comprises at least one additional thermoplastic material and/or has a specific gravity greater than 1.2.

The present invention is still further directed to a multilayer golf ball comprising: a core formed from a blend comprising polybutadiene and calcium carbonate, wherein the core has a COR of about 0.804 to about 0.806 and a compression of about 55; a cover layer formed from a blend of two or more ionomer resins, wherein said cover layer has a Shore D hardness of about 66 to about 68; and an intermediate layer disposed between the cover and the core, wherein the intermediate layer has a specific gravity of about 1.25 and is formed from a blend comprising about 5 to about 30 wt. % an ethylene methacrylic/acrylic acid copolymer, about 20 to about 40 wt. % ZnO; and up to about 60 wt. % polyetherester block copolymer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following terms that are used in this application are defined in terms of the enumerated ASTM tests:

Specific gravity ASTM D-297¹

Flexural (Flex) Modulus ASTM D-790²

Shore D Hardness ASTM D-2240

Shore C Hardness ASTM D-2240

As used herein, the terms "points" or "compression points" refer to the compression scale or the compression scale based on the ATTI Engineering Compression Tester. This scale, which is well known to those working in this field, is used in determining the relative compression of a core or ball. Some artisans use the Reihle compression scale instead of the standard compression scale. Based on disclosure in U.S. Pat. No. 5,368,304, column 20, lines 55-53 it appears that Reihle compression values can be converted to compression values through the use of the following equation:

    compression value=160-Reihle compression value.

As used herein, "COR" refers to Coefficient of Restitution, which is obtained by dividing a ball's rebound velocity by its initial (i.e. incoming) velocity. This test is performed by firing the samples out of an air cannon at a vertical steel plate over a range of test velocities (from 75 to 150 ft./sec.). A golf ball having a high COR dissipates a smaller fraction of its total energy when colliding with the plate and rebounding therefrom than does a ball with a lower COR. Unless otherwise noted, the COR values reported herein are the values determined at an incoming velocity of 125 ft./sec.

As used herein, the term "copolymer" refers to a polymer which is formed from two or more monomers.

As used herein, the term "pph" in connection with a batch formulation refers parts by weight of the constituent per hundred parts of the base composition (e.g. elastomer).

The present invention is directed to an improved multilayer golf ball which comprises a core, a cover, and at least one intermediate layer disposed between the core and the cover, wherein such golf ball provides a softer feel similar to a conventional wound ball, while also providing the distance, durability and spin rates of a conventional two-piece ball. As discussed in detail below, the improved multilayer golf ball of the present invention is provided by forming a ball having various structural components (e.g. cover, core, intermediate layer) each having desired properties and which may be formed from a variety of materials.

The Core

Many conventional two-piece "distance" golf balls are formed with cores having a high compression (e.g., greater than about 90) in order to achieve the desired high finished ball COR and initial velocity necessary to obtain long overall distance for the ball. Balls having such high compression cores typically have a hard feel when struck with a golf club.

However, the golf balls of the present invention are formed with a core having a low compression, but still exhibit a finished ball COR and initial velocity approaching that of conventional two-piece distance balls. Preferably, the cores employed in the golf balls of the present invention have a compression of less than about 60, more preferably about 45 to about 60 and most preferably about 50 to 55. Likewise, it is preferred that the finished balls made with such cores have a COR, measured at an inbound speed of 125 ft./sec., of about 0.795 to about 0.815, more preferably about 0.797 to about 0.812 and most preferably about 0.800 to about 0.810.

Additionally, it is preferred the core has a Shore C hardness of about 65 to about 80, more preferably about 68 to about 75 and most preferably about 72 to about 75.

The cores employed in the golf balls of the present invention preferably have a diameter of about 1.25 inches to about 1.51 inches, more preferably about 1.30 inches to about 1.48 inches and most preferably about 1.39 inches. The overall diameter of the core and the intermediate layer is about 84 percent to about 97 percent of the overall diameter of the finished ball.

A representative base composition for forming the cores employed in the present invention comprises polybutadiene and, in parts by weight based on 100 parts polybutadiene, 20-50 parts of a metal salt diacrylate, dimethacrylate, or monomethacrylate, preferably zinc diacrylate. The polybutadiene preferably has a cis 1,4 content of above about 90% and more preferably above about 96%. Commercial sources of polybutadiene include Shell 1220 manufactured by Shell Chemical, Neocis BR40 manufactured by Enichem Elastomers, and Ubepol BR150 manufactured by Ube Industries, Ltd. If desired, the polybutadiene can also be mixed with other elastomers known in the art, such as natural rubber, styrene butadiene, and/or isoprene in order to further modify the properties of the core. When a mixture of elastomers is used, the amounts of other constituents in the core composition are usually based on 100 parts by weight of the total elastomer mixture.

Metal salt diacrylates, dimethacrylates, and monomethacrylates suitable for use in the cores employed in this invention include those wherein the metal is magnesium, calcium, zinc, aluminum, sodium, lithium or nickel. Zinc diacrylate is preferred, because it provides golf balls with a high initial velocity in the USGA test. The zinc diacrylate can be of various grades of purity. For the purposes of this invention, the lower the quantity of zinc stearate present in the zinc diacrylate the higher the zinc diacrylate purity. Zinc diacrylate containing less than about 10% zinc stearate is preferable. More preferable is zinc diacrylate containing about 4-8% zinc stearate. Suitable, commercially available zinc diacrylates include those from Rockland React-Rite and Sartomer. The preferred concentrations of zinc diacrylate that can be used are 20-50 pph based upon 100 pph of polybutadiene or alternately, polybutadiene with a mixture of other elastomers that equal 100 pph.

Free radical initiators are used to promote cross-linking of the metal salt diacrylate, dimethacrylate, or monomethacrylate and the polybutadiene. Suitable free radical initiators for use in the invention include, but are not limited to peroxide compounds, such as dicumyl peroxide, 1,1-di(t-butylperoxy) 3,3,5-trimethyl cyclohexane, a-a bis (t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5 di (t-butylperoxy) hexane, or di-t-butyl peroxide, and mixtures thereof. Other useful initiators would be readily apparent to one of ordinary skill in the art without any need for experimentation. The initiator(s) at 100% activity are preferably added in an amount ranging between about 0.05 and 2.5 pph based upon 100 parts of butadiene, or butadiene mixed with one or more other elastomers. More preferably, the amount of initiator added ranges between about 0.15 and 2 pph and most preferably between about 0.25 and 1.5 pph.

Typical prior art golf ball cores incorporate 5 to 50 pph of zinc oxide in a zinc diacrylate-peroxide cure system that cross-links polybutadiene during the core molding process. However, in the present invention it is preferred that the zinc oxide (ZnO) in the core composition is eliminated in favor of calcium oxide (CaO). Cores produced from an admixture containing CaO have been found to exhibit desirable performance properties. In particular, when ZnO is replaced with CaO, it has been observed that the initial velocity and COR of the core is maintained, but the compression of the core is reduced by at least about 4 compression points on the standard compression scale, and may be reduced as much as 6 points. Additionally, the combination of the use of calcium oxide and a higher percentage of zinc diacrylate can be used to maintain the same compression as with the zinc oxide, but the initial velocity and COR is significantly increased. Thus, by using calcium oxide, either the core compression can be lowered and the initial velocity and COR maintained or the amount of zinc diacrylate can be increased so that the core compression is the same and the initial velocity and COR is increased.

Typically the calcium oxide added to the core-forming composition employed in the present invention is in the range of about 0.1 to 15, preferably 1 to 10, most preferably 1.25 to 5, parts calcium oxide per hundred parts (pph) of polybutadiene.

The core compositions employed in the present invention may also include fillers, added to the elastomeric composition to adjust the density and/or specific gravity of the core. As used herein, the term "fillers" includes any compound or composition that can be used to vary the density and other properties of the subject golf ball core. Fillers useful in the golf ball core according to the present invention include, for example, zinc oxide (in an amount significantly less than that which would be necessary without the addition of the calcium oxide), barium sulfate, and regrind (which is recycled core molding matrix ground to 30 mesh particle size). The amount and type of filler utilized is governed by the amount and weight of other ingredients in the composition, since a maximum golf ball weight of 1.620 ounces (45.92 gm) has been established by the USGA. Appropriate fillers generally used range in specific gravity from about 2.0 to 5.6. In the preferred golf ball, the amount of filler in the core is lower than that of a typical golf ball such that the specific gravity of the core is decreased.

The preferred range of specific gravities of the cores employed in the present invention is from about 1.0 to about 1.2, more preferably in the range of about 1.1 to about 1.18, depending upon the size of the core, cover, intermediate layer and finished ball, as well as the specific gravity of the cover and intermediate layer.

Other ingredients such as accelerators, e.g. tetra methylthiuram, processing aids, processing oils, plasticizers, dyes and pigments, antioxidants, as well as other additives well known to the skilled artisan may also be used in the present invention in amounts sufficient to achieve the purpose for which they are typically used.

The Intermediate Layer

The intermediate layer of the golf balls of the present invention is formed from a blend which comprises an ethylene methacrylic/acrylic acid copolymer. Below is a non-limiting example of the chemical structure for suitable ethylene methacrylic/acrylic acid copolymers: ##STR1## wherein x=50 to 99%; y=1 to 50%;

z=0 to 49%;

R₁ =H or CH₃ ; R₂ =CH₃ or isobornyl; and

n=0 to 12.

Specific acid-containing ethylene copolymers include ethylene/acrylic acid; ethylene/methacrylic acid; ethylene/acrylic acid/n- or isobutyl acrylate; ethylene/methacrylic acid/n- or iso-butyl acrylate; ethylene/acrylic acid/methyl acrylate; ethylene/methacrylic acid/methyl acrylate; ethylene/acrylic acid/iso-bornyl acrylate or methacrylate and ethylene/methacrylic acid/isobornyl acrylate or methacrylate. Suitable ethylene methacrylic/acrylic acid copolymers are sold commercially by DuPont under the tradename NUCREL®, with NUCREL® 960, NUCREL® RX9-1, and 010 being preferred.

In a preferred embodiment of the present invention, the intermediate layer is formed from a blend which comprises an ethylene methacrylic/acrylic acid copolymer and a second component which comprises a thermoplastic material. Suitable thermoplastic materials for use in the intermediate blend include, but are not limited to, polyesterester block copolymers, polyetherester block copolymers, polyetheramide block copolymers, ionomer resins, dynamically vulcanized thermoplastic elastomers, styrene-butadiene elastomers with functional groups such as maleic anhydride or sulfonic acid attached, thermoplastic polyurethanes, thermoplastic polyesters, polymers formed using a metallocene catalyst ("metallocene polymers") and/or blends thereof.

Suitable thermoplastic polyetheresters include materials which are commercially available from DuPont under the tradename Hytrel® and include Hytrel® 3078, Hytrel® G3548W and Hytrel® G4078W. Suitable thermoplastic polyetheramides are commercially available from Elf-Atochem under the tradename Pebax® and include Pebax® 2533, Pebax® 1205 and Pebax® 4033. Suitable thermoplastic ionomer resins include any number of olefinic based ionomers such as SURLYN® (DuPont) and IOTEKO (Exxon). Suitable dynamically vulcanized thermoplastic elastomers include Santoprene®, Sarlink®, Vyram®, Dytron® and Vistaflex®. Santoprene® is the trademark for a dynamically vulcanized PP/EPDM. Santoprene® 203-40 is an example of a preferred Santoprene® and is commercially available from Advanced Elastomer Systems. Examples of suitable functionalized styrene-butadiene elastomers, i.e., styrene-butadiene elastomers with functional groups such as maleic anhydride or sulfonic acid, include Kraton FG-1901x and FG-1921x, which are available from the Shell Corporation. Examples of suitable thermoplastic polyurethanes include Estane® 58133, Estane® 58134 and Estane® 58144, which are commercially available from the B.F. Goodrich Company. Suitable metallocene polymers, i.e., polymers formed with a metallocene catalyst include those commercially available from Sentinel Products of Hyannis, Mass. Suitable thermoplastic polyesters include polybutylene terephthalate.

Preferably, the second component of the intermediate layer blend comprises polyetherester block copolymer, with Hytrel® 3078 being a particularly preferred polyetherester block copolymer.

Many prior art intermediate layers generally have a specific gravity of about 1 or less. However, in a preferred embodiment, the intermediate layer employed in the golf balls of the present invention has a specific gravity greater than 1.2, preferably about 1.21 to about 1.30, more preferably about 1.23 to about 1.29 and most preferably about 1.27.

The desired specific gravity of the intermediate layer may be obtained by adding a filler such as barium sulfate, zinc oxide, titanium dioxide and combinations thereof to the intermediate layer blend. Zinc oxide is the preferred filler.

The intermediate layers of the present invention are formed from an intermediate layer blend comprising up to 100 percent by weight of an ethylene methacrylic/acrylic acid copolymer. In a preferred embodiment of the present invention, the intermediate layer is formed from a blend of about 1 to about 99 percent by weight ethylene methacrylic/acrylic acid copolymer, about 0 to about 75 percent by weight of the second thermoplastic component (as describe above) and about 0 to about 50 percent by weight zinc oxide. In one embodiment of the present invention, the intermediate layer is formed from a blend of about 10 to 50 percent by weight ethylene methacrylic/acrylic acid copolymer, 25 to 75 percent by weight of a second thermoplastic component and about 5 to about 40 percent by weight zinc oxide. In a most preferred embodiment of the present invention, the intermediate layer is formed from a blend of about 15 to about 25 percent by weight ethylene methacrylic/acrylic acid copolymer, about 50 to about 60 percent by weight of a second thermoplastic component and about 20 to about 30 percent by weight zinc oxide. In another embodiment of the invention, the second thermoplastic component is present in the intermediate layer blend in an amount of less than 50 percent by weight, and preferably 30 to 45 percent by weight.

A specific example of a most preferred intermediate blend composition comprises about 20 percent by weight Nucrel 960, about 57 percent by weight Hytrel 3078 and about 23 percent by weight zinc oxide.

The intermediate layer blend preferably has a flexural modulus of less than about 10,000 psi, more preferably about 5,000 to about 8,000 psi and most preferably bout 7,500 psi. Likewise, the intermediate layers employed in the golf balls of the present invention preferably have a Shore D hardness of about 35 to 50, more preferably about 37 to about 45 and most preferably about 40.

Preferably, the intermediate layer and core construction employed in the present invention have a compression of less than about 65, more preferably about 50 to about 65 and most preferably about 50 to 55.

The intermediate layers employed in the golf balls of the present invention preferably have a thickness from about 0.020 inches to about 0.125 inches, more preferably about 0.035 inches to about 0.085 inches and most preferably about 0.06 inches The outer diameter of the intermediate layer is preferably about 1.510 inches.

The Cover Layer

The cover layer of the present invention comprises at least one layer of a thermoplastic or thermosetting material. Any number of a wide variety of cover materials may be used in the present invention such as ionomer resins, polyurethanes, balata and blends thereof, with ionomer resins being preferred.

Ionomers, such as acid-containing ethylene copolymer ionomers, include E/X/Y copolymers where E is ethylene, X is a softening comonomer such as acrylate or methacrylate present in 0-50 (preferably 0-25, most preferably 0-2), weight percent of the polymer, and Y is acrylic or methacrylic acid present in 5-35 (preferably 10-35, most preferably 15-20) weight percent of the polymer, wherein the acid moiety is neutralized 1-90% (preferably at least 40%, most preferably at least about 60%) to form an ionomer by a cation such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc or aluminum, or a combination of such cations, lithium, sodium and zinc being the most preferred. Specific acid-containing ethylene copolymers include ethylene/acrylic acid, ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, and ethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containing ethylene copolymers include ethylene/methacrylic acid, ethylene/acrylic acid, ethylene/methacrylic acid/n-butyl acrylate, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methyl acrylate and ethylene/acrylic acid/methyl acrylate copolymers. The most preferred acid-containing ethylene copolymers are ethylene/methacrylic acid, ethylene/acrylic acid, ethylene/(meth)acrylic acid/n-butyl acrylate, ethylene/(meth)acrylic acid/ethyl acrylate, and ethylene/(meth)acrylic acid/methyl acrylate copolymers.

The manner in which these ionomers are made is well known in the art as described in e.g. U.S. Pat. No. 3,262,272. As mentioned above, ionomer resins are commercially available from DuPont Co. under the tradename SURLYN® and Exxon under the tradename IOTEK®.

As is well known in the art, ionomer resins may be blended in order to obtain a cover having desired characteristics. For this reason, it is preferable that the covers of the golf balls of the present invention be formed from a blend of two or more ionomer resins. A particularly preferred cover material for use in the present invention is formed from a blend of about 50 percent by weight SURLYN® 7940, about 47 percent by weight SURLYN® 8940 and about 3 percent by weight SURLYN® 8660.

The cover layers employed in the present invention preferably have a Shore D hardness of about 60 to about 72, more preferably about 65 to about 70 and most preferably about 68 to about 70.

The multi-layer golf ball of the invention can have an overall diameter of any size. Although the United States Golf Association (USGA) specifications limit the minimum size of a competition golf ball to 1.680 inches in diameter or more, there is no specification as to the maximum diameter. Moreover, golf balls of any size can be used for recreational play. The preferred diameter of the present golf balls is from about 1.680 inches to about 1.800 inches. The more preferred diameter is from about 1.680 inches to about 1.760 inches. The most preferred diameter is about 1.680 inches to about 1.740 inches.

The golf balls of the present invention have an overall maximum compression of about 85, preferably about 75 to about 85, more preferably about 80 to about 85 and most preferably about 82.

The golf balls of the present invention can be made by any conventional processes employed in the golf ball art. For example, the solid cores can be either injection or compression molded. The mantle layer is subsequently injection or compression molded about the core. It is important that the mantle material be able to sustain the temperatures applied during the application of the cover layer. The cover layer or layers are then injection or compression molded or cast about the mantle layer.

EXAMPLES Example 1

Table I below provides batch compositions for intermediate layer blends for forming the novel multilayer golf balls of the present invention. However, it is to be understood that the examples are only for illustrative purposes and in no manner is the present invention limited to the specific disclosures therein.

In particular, batch numbers 2-4 provide intermediate layer blends comprising NUCREL® 960, Hytrel® 3078 and zinc oxide used to form the intermediate layers of the golf balls of the present invention. Batch number 1 provides a control intermediate layer blend.

                  TABLE I                                                          ______________________________________                                         Intermediate Layer Batch Formulations                                                                            Flex.  Spec.                                 Batch #                                                                              % Nucrel 960                                                                              % Hytrel 3078                                                                             % ZnO Mod.   Grav.                                 ______________________________________                                         1     --         80%        20%   4210 psi                                                                              1.27                                  2     10         75%        15%   5560 psi                                                                              1.21                                  3     20         70%        10%   7710 psi                                                                              1.17                                  4     30         65%         5%   7250 psi                                                                              1.14                                  ______________________________________                                    

Example 2

Multilayer golf balls were made having intermediate layers formed from the batch compositions set forth in Table I. Several dozen golf balls were formed using each batch composition and subsequently tested for compression, spin rate and initial velocity.

The cores of all of the multilayer balls were formed by compression molding a blend of the batch formulation set forth in Table II below. All of the cores had a diameter of 1.39 inches and were measured to have compressions ranging from about 45 to about 55 and specific gravities of from about 1.134 to about 1.146.

                  TABLE II                                                         ______________________________________                                         Core Batch Formulation                                                                            Parts                                                       Material           Per Hundred                                                 ______________________________________                                         Polybutadiene (Shell 1220)                                                                        76.00                                                       Rubber (Enichem)   24.00                                                       Pigment            0.10                                                        Zinc Diacrylate    24.79                                                       Calcium Oxide      2.16                                                        Regrind            6.47                                                        Peroxide (Varox)   0.43                                                        Peroxide (EF-60) (DBDB)                                                                           0.16                                                        Filler             22.64                                                       Process Oil        1.50                                                        ______________________________________                                    

The intermediate layer blends of Table 1 were subsequently injection molded about the cores to form the intermediate layers of the balls having an outer diameter of about 1.51 inches.

All of the multilayer balls had a cover composition formed by injection molding a blend comprising 50% SURLYN® 7940 and 50% SURLYN® 8140 about the intermediate layers and were subsequently finished using conventional clear coating and buffing techniques. The finished golf balls had an outer diameter of about 1.68 inches. These balls were tested for initial velocity, compression, cover hardness and COR, the results of such tests are set forth in Table III below.

The balls were also tested for spin rate using a True Temper Test Machine configured to strike the balls with a Driver and an Eight Iron. Also tested for comparison purposes were conventional two piece "distance" balls (Titleist HP2 Distance and Pinnacle gold). The test data for all of these balls is set forth in Tables III-V below.

                  TABLE III                                                        ______________________________________                                                                           Cover.sup.2                                                                           COR.sup.3                                    Velocity.sup.1                                                                          Compression.sup.1                                                                         Weight.sup.1                                                                          Hardness                                                                              (@ 125                                Ball   (ft./sec.)                                                                              (Ball)     (ounces)                                                                              (Shore D)                                                                             ft/sec.)                              ______________________________________                                         Pinnacle.sup.4                                                                        252.5    95         1.605  68     0.809                                 Gold                                                                           HP2.sup.4                                                                             253      99         1.60   71     0.810                                 Distance                                                                       Ball 1 251.9    81         1.61   71     0.814                                 Ball 2 252.3    84         1.584  72     0.814                                 Ball 3 252.2    84         1.588  71     0.813                                 Ball 4 251.9    84         1.59   69     0.810                                 ______________________________________                                          .sup.1 Average based on results for 12 balls                                   .sup.2 Average based on results for 3 balls                                    .sup.3 Average based on results for 6 balls                                    .sup.4 Historical data for commercial balls                              

                  TABLE IV                                                         ______________________________________                                         Spin Rates For Driver (Average of 6 balls)                                     Club: Driver                                                                            Launch                       Club                                              Angle           Spin         Speed                                    Ball Type                                                                               (°)                                                                              std    (RPM)  std   (ft/sec)                                                                              std                               ______________________________________                                         Pinnacle Gold                                                                           9.1      0.3    3032   135   158.6  0.6                               HP2 Distance                                                                            9.0      0.3    2977   60    158.6  1.0                               Ball 1   9.1      0.5    2973   195   158.4  0.6                               Ball 2   9.1      0.5    3001   66    158.9  0.7                               Ball 3   9.1      0.4    3006   121   158.9  0.8                               Ball 4   9.0      0.3    3007   140   159.0  0.6                               ______________________________________                                    

                  TABLE V                                                          ______________________________________                                         Spin Rate For Driver (Average of 6 balls)                                      Club: 8 Iron                                                                            Launch                       Club                                              Angle           Spin         Speed                                    Ball Type                                                                               (°)                                                                              std    (RPM)  std   (ft/sec)                                                                              std                               ______________________________________                                         Pinnacle Gold                                                                           19.2     0.4    8160   218   116.4  0.1                               HP2 Distance                                                                            19.4     0.5    8375   171   116.3  1.3                               Ball 1   19.2     0.5    7970   246   116.2  0.7                               Ball 3   19.3     0.2    7972   168   116.5  0.9                               Ball 4   19.4     0.3    7940   171   117.0  1.3                               ______________________________________                                    

As shown by results reported in Tables III-V, golf balls having an intermediate layer comprising Nucrel 960, Hytrel 3078 and ZnO have a high initial velocity and low spin rate. Moreover, the balls of the present invention have initial velocities approaching those of conventional two-piece "distance" balls, but have a considerably lower compression, which provides a much softer feel, more like a wound ball. Still further, these balls are easy to manufacture compared to the conventional wound ball. Thus, these balls provide the advantages of two piece "distance" balls with low spin rates and high velocity, but also provide a softer feel than such balls.

Example 3

Multilayer golf balls were made having intermediate layers formed from a blend comprising 20% Nucrel 960, 57% Hytrel 3078 and 23% Zinc Oxide. This intermediate layer blend was injection molded about cores formed from the batch formulation set forth in Table II. A cover was formed by injection molding a blend of 50% SURLYN® 7940, 47% SURLYN® 8940 and 3% SURLYN® 8660 around the intermediate layer and subsequently finishing the balls using conventional clear coating and buffing techniques.

The balls were tested for initial velocity, compression, cover hardness and COR, as well as for spin rate when struck by a Driver and Eight Iron using a True Temper Test Machine. The results of such tests are set forth below in Tables VI and VII below.

                  TABLE VI                                                         ______________________________________                                                                    Cover.sup.2                                                                           COR.sup.3                                    Velocity.sup.1                                                                        Compression.sup.1                                                                         Weight.sup.1                                                                            Hardness                                                                              (@ 125                                                                               Specific                               (ft/sec)                                                                              (Ball)     (Ounces) (Shore D)                                                                             ft/sec.)                                                                             Gravity                                ______________________________________                                         251.5  82         1.607    69     0.801 1.27                                   ______________________________________                                          .sup.1 Average based on results for 12 balls                                   .sup.2 Average based on results for 3 balls                                    .sup.3 Average based on results for 6 balls                              

                  TABLE VII                                                        ______________________________________                                                                              Club                                             Launch °  Spin         Speed                                     Club   Angle     Std.   (RPM)  Std.  (ft/sec)                                                                              Std.                               ______________________________________                                         Driver 9.2°                                                                              0.5    3015   221   160.3  0.7                                8 Iron 19.3°                                                                             0.6    7807   252   115.6  0.8                                ______________________________________                                     

We claim:
 1. A golf ball comprising:(a) a core formed from a blend comprising polybutadiene, wherein the core has a compression of no greater than about 60; (b) a cover layer having a Shore D hardness of about 60 to about 72; (c) an intermediate layer disposed between the cover and the core, wherein the intermediate layer is formed from a blend comprising an ethylene methacrylic/acrylic acid copolymer having the formula consisting essentially of: ##STR2## wherein x=50 to 99%; y=1 to 50%; z=0 to 49%; R₁ =H or CH₃ ; R₂ =methyl, butyl, an isobornyl; and n=0 to 12; and wherein the golf ball has a COR measured at 125 ft./sec. of about 0.795 to about 0.815.
 2. The golf ball of claim 1, wherein the intermediate layer has a specific gravity of greater than 1.2.
 3. The golf ball of claim 1, wherein the intermediate layer blend further comprises a second component, wherein said second component is a thermoplastic material.
 4. The golf ball of claim 3, wherein the second component is selected from the group consisting of polyesterester block copolymers, polyetherester block copolymers, polyetheramide block copolymers, ionomer resins, dynamically vulcanized thermoplastic elastomers, styrene-butadiene elastomers with functional groups attached, thermoplastic polyurethanes, thermoplastic polyesters, polymers formed using a metallocene catalyst and blends thereof.
 5. The golf ball of claim 4, wherein the second component comprises a polyetherester block copolymer.
 6. The golf ball of claim 5, wherein the intermediate layer blend further comprises a filler.
 7. The golf ball of claim 6, wherein the second thermoplastic component comprises polyetherester block copolymer and the filler comprises zinc oxide.
 8. The golf ball of claim 7, wherein the intermediate layer blend comprises about 10 to about 50 percent by weight ethylene methacrylic/acrylic acid copolymer, about 25 to about 75 percent by weight second thermoplastic component and about 5 to about 40 percent by weight filler.
 9. The golf ball of claim 7, wherein the intermediate layer blend comprises about 15 to about 25 percent by weight ethylene methacrylic/acrylic acid copolymer, about 50 to about 60 percent by weight second thermoplastic component and about 20 to about 30 percent by weight filler.
 10. The golf ball of claim 1, wherein the intermediate layer blend has a specific gravity of about 1.21 to about 1.30.
 11. The golf ball of claim 1, wherein the intermediate layer has a Shore D hardness of about 35 to about 50 and a flexural modulus of about 5,000 psi to about 8,000 psi.
 12. The golf ball of claim 1, wherein the core blend further comprises calcium oxide.
 13. The golf ball of claim 1, wherein the core has a Shore C hardness of about 65 to about
 80. 14. The golf ball of claim 1, wherein the golf ball has a compression of no greater than
 85. 15. A golf ball comprising:(a) a core formed from a blend comprising polybutadiene, wherein the core has a compression of less than about 55; (b) a cover layer formed from a blend of two or more ionomer resins, wherein said cover layer has a Shore D hardness of about 66 to about 70; (c) an intermediate layer disposed between the cover and the core, wherein the intermediate layer has a specific gravity of about 1.27 and is formed from a blend comprising:(i) about 15 to about 25 wt. % an ethylene methacrylic/acrylic acid copolymer having the formula consisting essentially of: ##STR3## wherein x=50 to 99%; y=1 to 50%; z=0 to 49%; R₁ =H or CH₃ ; R₂ =methyl, butyl, and isobornyl; and n=0 to 12; (ii) about 20 to about 30 wt. % ZnO; and (iii) up to about 60 wt. % polyetherester block copolymer; and wherein the golf ball has a COR of about 0.804 to about 0.806.
 16. The golf ball of claim 15, wherein:(a) the core blend further comprises calcium oxide; (b) the intermediate layer is formed from a blend comprising:(i) about 20 wt. % copolymer of ethylene and methacrylic acid; (ii) about 25 wt. % ZnO; (iii) about 55 wt. % polyetherester block copolymer.
 17. The golf ball of claim 16, wherein the intermediate layer has a Shore D hardness of about 40 and a flexural modulus of about 7500 psi, the core has a Shore C hardness of about 75 and the golf ball has a compression of about
 82. 18. A golf ball comprising a core, a cover layer having a Shore D hardness of about 60 to about 68, and an intermediate layer disposed between the cover and the core, wherein the intermediate layer is formed from a blend comprising an ethylene methacrylic/acrylic acid copolymer having the formula consisting essentially of: ##STR4## wherein x=50 to 99%; y=1 to 50%; z=0 to 49%; R₁ =H or CH₃ ; R₂ =methyl, butyl, and isobornyl; and n=0 to 12; andand a second component comprising a thermoplastic material. 